Code position modulation system and method for multiple user satellite communications

• US 5,313,457 A
• Filed: 04/14/1992
• Issued: 05/17/1994
• Est. Priority Date: 04/14/1992
• Status: Expired due to Fees

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Babitch, Daniel, Hostetter, George R.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): TON, DANG T
• Application Number:
  US07/868,985
• Time in Patent Office: 763 Days
• Field of Search: 370/18, 370/17, 370/50, 370/69.1, 370/70, 370/105.4, 370/105.5, 370/110.4, 370/105.1, 370/95.1, 370/95.3, 375/1, 375/116, 375/115, 375/118, 375/38, 375/40, 375/58, 375/60, 375/101, 375/107, 375/108, 375/111, 375/112, 375/113, 375/56, 375/42, 455/50.1, 455/54.1, 455/59, 455/63, 455/12.1, 455/32.1, 358/12, 358/142, 358/143, 371/43, 371/46, 381/2, 381/13, 381/14, 379/59, 379/60
• US Class Current: 370/320
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 14/026 using pulse time characteristics modulation, e.g. width, position, interval
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 3/0605 Special codes used as synchronising signal

Abstract

An embodiment of the present invention is a communications system for multiple users sharing the same maximal length code (MLC) in a code position modulation multiple access environment. A 1023 chip length code is transmitted with reference to an independent coordinated time source. The code repeats every time after 1023 chips have been transmitted. The MLC will begin each time period with the first through 1023^rd chip, depending on the data to be sent and the identity of the user transmitting it. The chips belong to the MLC that were not sent at the beginning of a time period are sent at the end to complete the MLC each time period in a wrap around fashion. Each time period can be aribtrarily divided into subsections embracing, for example, sixteen chip times. When so divided, more than sixty subsections are possible from one 1023 chip MLC. Respective users are each assigned a subsection. If the transmitted MLC begins on one of the sixteen chip time slots in a particular user'"'"'s assigned subsection, the chip time slot that the MLC does begin on will be interpreted as communicating four bits of data, 0000 . . . 1111.

Claims

1. A non-multiplexing method of code position modulation multiple access (CPMMA) communications, the method comprising the steps of:

defining a maximal length code (MLC) having "n" number of chips C₀ through C_n ;

defining a time period having "n" number of subperiods t_i beginning at times t₀ through t_n, each subperiod having at least one code chips;

assigning said "n" subperiods to an "n" number of different user transmitters;

transmitting for respective users said MLC in chip sequence such that a first chip of said MLC starts within said time period and within their assigned subperiods, wherein a correlation peak of each transmitter'"'"'s code falls within an assigned subperiod as seen at a master/hub receiver and enabling a continuous sending of code from each transmitter with non-overlapping correlation peaks that are discriminable from one another;

modulating for respective users the transmission of each MLC in chip sequence in respective subperiods such that a particular chip c_m that begins in a particular subperiod is controlled by a data-to-be-transmitted, the modulation and transmitting being such that the c_m through c_n chip are immediately followed by the chips C₀ through C_m-1.

2. The method of claim 1, further comprising the step of:

phase modulating said user transmitters with at least one of a group of modulation methods that includes shaped binary phase shift keying, unshaped binary phase shift keying, and continuous phase modulation.

3. The method of claim 1, further comprising the step of:

demodulating the transmission of each MLC to detect which particular chip c_m begins in a particular time period and to detect one of "m" phase states.

4. A communication system for supporting continuous and simultaneous communication links between a plurality of user stations, comprising:

a plurality of code position modulation multiple access (CPMMA) transmitters each sharing a single maximal length code (MLC) comprised of a fixed length of code chips and differing in their transmission carrier signals by a starting time each CPMMA transmitter begins its transmission of said MLC in any one of a plurality of code chip positions equal in number to the number of code chips in said MLC; and

at least one CPMMA receiver having means for selecting which CPMMA transmitter to tune to based on said starting time, measured in relative code chip position in said single MLC, that a particular CPMMA transmitter begins its transmission of said MLC.

5. The system of claim 4, wherein:

each CPMMA transmitter of the plurality of CPMMA transmitter is associated in a pair with one of the CPMMA receivers and said pairs of CPMMA transmitters and receivers are fixed at separate user locations with interconnecting user links.

6. The system of claim 4, wherein:

each CPMMA transmitter of the plurality of CPMMA transmitters includes means for receiving a common time base signal from orbiting global positioning system (GPS) satellites connected to synchronizing means for beginning a transmission of said MLC from a particular CPMMA transmitter at a time relative to said time base signal.